Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260925

Area Forecast Discussion
325 AM CST Thu Feb 26 2015

.SHORT TERM...(Today)

08z/2am surface analysis shows 1012mb low over southern Missouri,
with light snow falling from the Saint Louis area northeastward
across much of central Illinois. The exception is along/south of the
I-70 corridor, where the atmospheric column remains unsaturated
and snow has been unable to reach the ground thus far.  Low will
continue to dissipate this morning: however, high-res models
suggest the snow will persist through midday before gradually
tapering off and coming to an end from west to east during the
afternoon.  Will carry categorical PoPs this morning from the
Illinois River eastward to the I-57 corridor where snow will be
ongoing.  Further southeast, will only mention chance PoPs across
the far SE CWA around Olney and Lawrenceville as precip will tend
to diminish as it tries to work into this area later this morning.
Additional accumulations will be minimal, generally one half inch
or less.  Breezy and colder conditions will develop behind the
departing low.  High temperatures will mainly be in the teens and
lower 20s, but wind-chill values will hover in the single digits.


.LONG TERM...(Tonight through Wednesday)

1044mb high currently over Saskatchewan will build southeastward
tonight, reaching Iowa by 12z Fri.  As the high approaches, skies
will clear from west to east and winds will subside.  Given these
conditions and the presence of a fresh snow cover across the W/NW
KILX CWA, radiational cooling will result in bitterly cold sub-zero
overnight lows.  Even though winds will become light, they will
remain just strong enough to create wind-chill readings from 10 to
20 below zero.  End result will likely be a Wind Chill Advisory
across much of the area, but will hold off issuing until after the
current Winter Weather Advisory for snow expires this morning.

After a period of cold/dry weather Friday into Saturday, things get
more active through the remainder of the extended as southwesterly
flow develops across the central CONUS.  This flow regime will bring
warmer, but more unsettled conditions into Illinois beginning late
this weekend and persisting into the middle of next week.  A
baroclinic zone will lift northward into central/southern Illinois
and become stationary as it becomes parallel with the upper-level
flow.  Numerous waves are expected to track along the boundary,
setting the stage for periodic rounds of precip.  The first wave
will arrive Saturday night into Sunday, with models in very good
agreement that most of the precip across the area will be in the
form of snow.  Will carry likely PoPs Saturday night and Sunday
accordingly.  With ample deep-layer moisture flowing northward into
the region and strong lift focusing along/north of the boundary,
several inches of snow will accumulate across central Illinois.
It is still too early to pinpoint exact totals, but amounts in
excess of 4 inches are likely north of the I-70 corridor.

The snow will taper off an come to an end Sunday night as the
initial wave passes off to the east and the boundary gets
temporarily pushed further southward.  High pressure will build into
the area on Monday, bringing cold and dry conditions.  As the high
departs, a stronger wave will quickly approach from the southwest
Monday night into Tuesday.  While model discrepancies still exist,
the 00z Feb 26 suite has come into better agreement with surface low
pressure developing in the lee of the Rockies in eastern Colorado
Monday evening tracking northeastward into northern Indiana by
Tuesday night.  This particular track will make for a challenging
precip type forecast across central Illinois as quite a bit of WAA
will occur ahead of the system.  GFS forecast soundings show a
pronounced warm layer developing aloft, with max temps reaching the
4-8C range by late Monday night.  This would strongly suggest liquid
precip.  The problem will be with the low-level thermal profile, as a
significant snow cover from the Saturday night/Sunday wave will
likely keep surface temps colder than models currently indicate.
Given this, think freezing rain/sleet may be an issue Monday night
into Tuesday morning before low-level temps warm sufficiently to
support all rain by midday Tuesday.  High temps on Tuesday will
range from the upper 30s far north to the middle 40s south of I-70.
As the low pulls away, colder air will filter back into the region
Tuesday night into Wednesday.  Could see a little light snow before
the precip ends Tuesday night, with cold/dry conditions returning for


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)

Light snow is slowly overspreading all the TAF sites and by 06z,
it should be snowing at all locations. IFR conditions should be
occurring at all locations, except for SPI and DEC, but will keep
a TEMPO group for IFR conditions for those two sites overnight. As
the system continues to move southeast overnight conditions will
gradually improve. Upstream observations indicate that MVFR type
conditions will occur during the morning hours and into the
afternoon. Light snow or flurries will still be possible through
the afternoon, but then end during the evening hours. Winds will
become northerly and last through the TAF period.





LONG TERM...Barnes
AVIATION...Auten is the U.S. government's official web portal to all federal, state and local government web resources and services.